Dr. Bainter is a board-certified ophthalmologist. She received her BA from Pomona College in Claremont, CA, and her MD from the University of Colorado in Denver, CO. She completed an internal medicine internship at St. Joseph Hospital in Denver, CO, followed by an ophthalmology residency and a cornea and external disease fellowship, both at the University of Colorado. She became board certified by the American Board of Ophthalmology in 1998 and recertified in 2008. She is a fellow of the American Academy of Ophthalmology. Dr. Bainter practices general ophthalmology including cataract surgery and management of corneal and anterior segment diseases. She has volunteered in eye clinics in the Dominican Republic and Bosnia. She currently practices at One to One Eye Care in San Diego, CA.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
Astigmatism is an irregularity in the way light is focused (refracted) by the eye. Most commonly, astigmatism is a result of variations in the curvature of the cornea of the eye. However, astigmatism can also be caused by similar irregularities in the curvature of the lens of the eye.
Astigmatism is classified as “regular” if the irregularity is easily corrected with glasses or contact lenses, such as when the cornea takes on the shape of a football (steeper in one axis, flatter in the opposite axis) as opposed to a sphere. It is classified as “irregular” if the curvature is more variable, or if the steepest portion is off-center.
What are the risk factors for astigmatism?
Most regular corneal astigmatism develops for unknown reasons and may be inherited. Some astigmatism can be acquired when the cornea's curvature is altered by outside forces such as the weight of a droopy eyelid, a suture, a scar, or a condition that alters the cornea's structure. This occurs, for example, in a condition called keratoconus, whereby the cornea becomes cone-shaped.
The symptom of astigmatism is poorly-focused vision that causes blurring. This blurring can often be corrected with glasses or contact lenses. The principal finding in examining for astigmatism is an irregular curvature (such as football shape) to the cornea and/or lens. This may require specialized testing to detect and measure.
How is astigmatism diagnosed?
Astigmatism is diagnosed during the measurement for glasses (refraction). The eye's overall astigmatism can be measured objectively by a manual technique using a device called a retinoscope, or automatically with an autorefractor machine. Subjectively, a patient can determine the necessary astigmatism correction by choosing from several different powers of lenses. The various lens powers are presented to the patient while viewing a chart through a phoropter.
Distinguishing which portion of the astigmatism is arising from the cornea versus arising from the lens can be important, particularly when fitting a contact lens or planning a surgical procedure. This can be done by examining the shape of the cornea with studies such as topography and keratometry. Wavefront analysis is another tool that is useful in evaluating irregularities in the way the eye focuses light.
If the astigmatism is found to be irregular, further studies may be necessary. A thorough eye examination including a slit lamp examination can be used to detect external forces that are warping the cornea (such as drooping eyelid, suture, scar, and others). If the cornea's shape is irregular due to a suspected corneal disease (such as keratoconus, pellucid marginal degeneration, post-LASIK ectasia, and more) further studies may be necessary to confirm the suspected diagnosis.
Reviewed by William C. Shiel Jr., MD, FACP, FACR on 6/25/2013
Almost all degrees of astigmatism can be corrected with properly prescribed eyeglasses or contact lenses. For a person with only a slight degree of astigmatism, corrective lenses may not be needed at all, as long as other conditions such as nearsightedness or farsightedness are not present. If the astigmatism is moderate to high, however, corrective lenses are probably needed.